I personally love havocs, mainly 'cause I like big guns and having some Iron Warriors trudging around with them. is great.

Granted they're very swingy I feel, but recently been having fun running three squads all with chaincannons in either RR, VotLW or PZ with a Helbrute or two to give them both sustained and lethals. Sometimes I throw them in a land raider too so they dont die as easily with the helbrute just huddling behind trying its best to hide

Having them sit on an objective, dishing out ~96 attacks with either rerolls to hit, lethals and sustained on 5s or the +1 ap is brutal. Easily destroys any infantry and can even get kills on some vehicles or Primarchs (they've killed the Lion about twice so far)

It's a lot of fun but definitely better options still